feat(后台设置): 设置页重排成网站、班级、开关、判题机几块，保存挪到右上角；班级按年级分组不用再拖；判题机写出多久没动静；AI 小助手（MaxKB 挂件）整个删掉

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

apps/web/src/env.d.ts

@@ -2,7 +2,6 @@
 
 interface ImportMetaEnv {
   readonly PUBLIC_ENV: string
-  readonly PUBLIC_MAXKB_URL: string
   readonly PUBLIC_CODE_URL: string
   readonly PUBLIC_ICONIFY_URL: string
 }